Simple HTTP statistics timer in F#

http_stopwatch.fs

open System
open System.IO
open System.Net
open System.Diagnostics


let track (url:string) (log:string) =
  while true do
    let stopwatch = new Stopwatch()
    stopwatch.Start()

    let error = ref (None : string option)
    let status = ref 0
    try
      let request = WebRequest.Create(url) :?> HttpWebRequest
      use response = request.GetResponse() :?> HttpWebResponse
      status := int response.StatusCode
    with ex ->
      error := Some ex.Message

    stopwatch.Stop()


    try
      printfn "%A - elapsed %A" System.DateTime.Now stopwatch.Elapsed
      use file = File.AppendText log
      file.WriteLine( sprintf "\"%A\",\"%A\",\"%s\"" System.DateTime.Now stopwatch.Elapsed.Milliseconds (defaultArg error.Value "") )
      file.Close()
    with ex ->
      printfn "ERROR: %s" ex.Message

    System.Threading.Thread.Sleep INTERVAL